1. Field of the Invention
The present invention relates to a radiation image information reading apparatus capable of simultaneously performing reading and erasing processes with respect to a double-sided stimulable phosphor sheet (also referred to as a stimulable phosphor sheet) on which radiation image information can be recorded on both sides.
2. Description of the Related Art
In a radiation image information reading apparatus for producing a radiation-transmitted image of an object, an easy-to-handle stimulable phosphor sheet (accelerated phosphor sheet) is finding wider use as an alternative to a conventional X-ray.
When a certain phosphor is exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays, ultraviolet rays, etc., the phosphor stores a part of the energy of the radiation. When the phosphor exposed to the radiation is then exposed to stimulating rays such as visible light, etc., the phosphor emits accelerated light in proportion to the stored energy of the radiation. A phosphor which exhibits such a property is referred to as a "stimulable phosphor" or a "stimulable phosphor".
In the radiation image information reading apparatus, the stimulable phosphor sheet exposed to the radiation through an object such as a human body is scanned with stimulating rays such as a laser beam, so that the stimulable phosphor sheet emits accelerated light indicative of the radiation image. The emitted light is then photoelectrically read to produce an image signal. Thereafter, image information generated based on the so-produced image signal is recorded as a visible image on a recording medium such as a photographic film or displayed as a visible image on a CRT or the like.
In this case, the stimulable phosphor sheet may simply bear the image information until it is scanned with the stimulating rays. It is desirable however that the image information can be erased from the stimulable phosphor sheet after completion of its scanning so the stimulable phosphor sheet can be used again in a process for recording image information thereon. For this purpose, for example, there has been proposed an apparatus of such a type that an erasing unit is located downstream of the stimulable .phosphor sheet which is fed in an auxiliary scanning direction, as seen from a position where the stimulable phosphor sheet is scanned, and the stimulable phosphor sheet is exposed to the stimulating rays while feeding the stimulable phosphor sheet discharged from a cassette in the auxiliary scanning direction, followed by scanning with the stimulating rays thereby emitting light for reading photoelectrically, i.e., detecting the so-emitted light to produce an image signal indicative of image information, followed by execution of a process for erasing the image information from the stimulable phosphor sheet under the control of the erasing unit (see Japanese Patent Application No. 60-264482).
However, the processes for reading the radiation image information from the stimulable phosphor sheet and erasing the same therefrom are performed in a separate manner in the above-described radiation image information reading apparatus. Therefore, each of the radiation image information reading/erasing processing operations cannot efficiently be performed in its entirety.
Further, the scanning unit and the erasing unit are arranged side by side along the auxiliary scanning direction, thereby causing a problem that both the total radiation image information reading apparatus and the space it takes become very large.